The present invention relates to a new and improved construction of a thermostatic expansible material-working element having a housing filled with an expansible material or substance and a substantially pin-shaped work piston which is pointed at one end, this work piston extending with its pointed end through an opening in the housing into the internal compartment thereof and upon thermal expansion of the expansible material such piston is pushed by the expansible material out of the housing.
Such thermostatic expansible material-working elements are components which according to a temperature characteristic --dependent upon the selection of the expansible material or substance-- produce at their work piston mechanically accessible adjustment forces, and for the size of the stroke in a certain temperature range between a response temperature and an upper boundary temperature there exists a well defined dependency.
Owing to their small space requirements and because of the relatively great force which such working elements are capable of producing such are to some extent installed as servo-motors in remotely controlled installations or, however, for the temperature-dependent actuation of valves are installed at or in such valves themselves.
The reliability of such work or working elements is only then guaranteed when and as long as the elements are free of leakage, i.e., as long as the quantity of expansible material which once has been filled into the housing remains constant. As the expansible material or substance there are generally used oils or waxes which exxperience an increase in volume during their transition from the solid phase into the liquid phase. The flowing-out or leakage of even only a fraction of the expansible material from the housing basically alters the temperature characteristic of the working element and in most instances renders the same unusable.
Therefore, the greatest attention has been paid to the problem of sealing the internal compartment or space of the housing relative to the surrounding external space in the case of all previously known working elements of the aforementioned type. However, it was not possible up to now to provide a seal which retained its sealing properties over an unlimited period of use of the working element. The susceptibility to aging of the heretofore known working elements resides in the fact that as the seal between the internal compartment of the housing and the piston, the latter of which extends into such internal compartment and of necessity also protrudes out of the housing, there were provided components formed of rubber-like substances. These substances are only resistant to aging to a limited extent, particularly because of the frequent temperature changes to which the working elements are of course subjected and for which they were designed. This has been amply proven by the heretofore known working elements of the previously mentioned type.
For instance for the working element which has been taught to the art in U.S. Pat. No. 3,403,560 the expansible material or substance is a wax, preferably a mineral wax. It fills the ring-shaped space between the inner wall of the housing and the outside of a sheath formed of rubber which tightly surrounds the pointed (inner) end of the work piston. The sheath or case itself possesses at its open end a marginal flange which is clamped between a shoulder of the housing and a flanged housing cover which also possesses the throughpassage opening for the work piston. In this construction the marginal flange serves as the seal.
Also in the thermostatic actuation element taught in the German Pat. No. 1,958,563 the throughpassage opening for the work piston is formed in the housing cover, which at the same time fixedly clamps at its outer edge a seal which encloses in a packing gland-like manner the work piston at least at the region of the passage through the opening.
The same holds true for the work element which has become known from the German Pat. No. 1,473,231, wherein not only the sheath which tightly encloses the work piston is formed of elastic material, rather also a circular cord seal which surrounds the piston at the region of the opening.
With the work element according to the German Pat. 1,573,384 the piston indeed engages directly into the expansible substance, but its throughpassage location out of the housing is sealed with a pre-biased seal in the manner of a stuffing-box or packing gland.
In all of the above-mentioned patent publications a particularly great significance has been attributed to the construction of the seal between the housing and the work piston at its throughpassage location. However, in practice it was not heretofore possible to provide a solution of the problem which was satisfactory over a longer time span, regardless whether there is employed a liquid or solid expansible substance, or such which in the working or operating range transform from the solid phase into the liquid phase or vice versa.